The invention relates generally to foam and foam generating systems, and more particularly to an aqueous foam generating system and method for generating a foam that exhibits wet-to-dry transition times on the order of days rather than minutes or hours.
A foam can be described as a mass of gas bubbles in a liquid-film matrix. Two factors control the ability of a liquid to foam under mechanical agitation: (a) surface tension, and (b) the presence of impurities in the liquid itself. Surface tension is the condition used to describe the net result of attractive intramolecular forces (i.e., dipolar and Van der Waals forces) over the surface of a liquid and is measured in dynes/cm or Joules/cm2. The net result of unbalanced molecular forces near the surface provide the necessary additional energy to provide an increased liquid surface area. However, the increased liquid surface area that could be obtained through the surface tension effect is minimal even with mechanical agitation unless a surfactant is added.
Surfactants can be hydrophobic or hydrophilic. For the case of hydrophobic surfactants, the surfactant molecules migrate to the air-water interface because the surface is energetically favored for the surfactant as compared to the water molecules. As a result of this migration, the surface tension of the water/surfactant system is significantly decreased from that of water alone. From a thermodynamic standpoint, the addition of the surface film actually decreases the total internal energy of the system to the point that a metastable system (i.e., foam) can exist by virtue of the reduced tensile force acting on each foam cell. However, due to the low viscosity of water, a wet-cell to dry-cell transition takes place within minutes of creation of an aqueous foam. For the above reasons, conventional aqueous foams are not suitable for uses such as explosive blast containment, firefighting, toxic substance containment, frost damage prevention for crops/plants, etc., since the desirable water mass is lost within minutes of foam placement.
Accordingly, it is an object of the present invention to provide a foam having an extended wet-to-dry transition time.
Another object of the present invention is to provide a slow draining aqueous foam.
Still another object of the present invention is to provide a method of making an aqueous foam.
Yet another object of the present invention is to provide an aqueous foam generation system.
A further object of the present invention is to provide a method and system of making an aqueous foam that has wet-to-dry transition times on the order of days.
Yet another object of the present invention is to provide an improved aqueous foam that can be made using conventional foam making equipment.
Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings.
In accordance with the present invention, an aqueous foam generating system and method are provided. A first solution provides particles of a carbomer resin encapsulated within an anhydrous, non-polar, organic hydrophobic surfactant. A second solution provides a neutralizing liquid having a ph in the range of approximately 5-11. The second solution must be capable of ionizing the carbomer resin. The second solution is pumped into an eductor which draws a volumetric portion of the first solution into the second solution being pumped through the eductor. As a result, a mixture of the first solution and second solution exits the eductor. An aerator coupled to the output of the eductor sprays the mixture to form an aqueous foam. Some time after the foam is formed and deployed, a chemical reaction takes place. This chemical reaction increases the viscosity of water and modifies its flow characteristics from a Newtonian flow to a high-yield-plastic flow at the foam unit cell with no density changes. Wet-to-dry foam transition of the improved foam system occurs mainly through surface evaporation which is a very slow process.